For the Yukawa sector we will assume the concept of single operator dominance (cf. [1]}, [2]}), i.e. we will assume that each entry of the Yukawa matrices is governed by one singlet GUT operator giving the dominant contribution to this entry. Furthermore, we will assume that the Yukawa matrices have hierarchical structure. Focusing on the GUT scale Yukawa matrix \(Y_{\overline{5}}\)  leading simultaneously to the masses for the down-type quarks and charged leptons, it follows that the second and third family masses stem dominantly from the GUT operators \({\cal O}_2\)  and \({\cal O}_3\)  dominating the 22 and 33 positions of the hierarchical Yukawa matrix, i.e.:
\(Y_{\overline{5}}=\begin{pmatrix}0&& 0 && 0 \\0 && {\cal O}_2 && 0 \\0 && 0 && {\cal O}_3\end{pmatrix} + \dots \:,\) 
